The present invention relates to a method for the controlled addition of an additive to the fuel supply of a vehicle internal combustion engine. Such an additive supply system is particularly useful, for example, with a diesel engine equipped with an exhaust particulate filter, which can be burned free more effectively by the addition of a fuel additive.
Additive metering of this kind is known from DEC-36 26 419, in which a check is made every time the vehicle remains stationary for a predetermined time period as to whether an increase in the fuel level occurs. If an increase is detected, it is treated as an indication of an addition of fuel, and consequently an addition of additive proportional to the increase in the fuel level is performed. In this method, the addition of additive can be carried out while the vehicle is stationary. However, since the interior noise level while the vehicle is stationary is usually extremely low in vehicles with a high level of finish, even with the engine running, the noise caused by addition of additive (the pump delivering the additive to the fuel) is often considered to be an unusual undesired noise. It is an important object of the present invention to provide an improvement particularly in this regard. It is a further object of the invention to eliminate or at least minimize measurement errors, which can occur due to a tilted position of the vehicle during refuelling if the level comparison measurements have not been taken exclusively in the same position of the vehicle.
This complex of problems is solved according to the invention, in which measured values for the fuel level, averaged continuously from individual measured values for a certain period of time, are in each case compared to one another successively. That is, the last average value is compared to the penultimate average value, while the vehicle is in motion, the driving condition being detected by a speed sensor (known per se). Any difference which exceeds a certain predetermined tolerance level in the course of this comparison is evaluated as a corresponding increase in the fuel volume, and thus causes an addition of additive proportional to the increase in the fuel supply, by means of a pump. It is not necessary for the vehicle to be stationary in this method. On the contrary, it would be possible to refuel the vehicle during driving, in which case the addition of additive would be carried out in the same manner.
In the method for the addition of additive according to the invention, because level measured values averaged over a plurality of time intervals are used for evaluation only during driving, metering can necessarily only occur during driving. This has the advantage that, due to the higher noise level in the interior of the vehicle in driving operation (compared to that when the vehicle is stationary), the noise emanating from the metering pump is either imperceptible to the driver, or is at least not perceived as an annoyance.
To ensure that the noise of the metering pump is not troublesome in the interior of the vehicle, its activation is also made dependent on the attainment of a predetermined driving speed.
Incorrect diagnoses due to measurements with at times differing tilted positions of the vehicle are largely eliminated by evaluating only measured values averaged over a plurality of time intervals.
The individual measurements carried out only while the vehicle is in motion can, for example, be performed at time intervals of 0.01 time units/sec. About 10,000 time intervals can be used for averaging in each case. The averaged values are compared for the purpose of detecting an increase in the fuel level, the comparison in each case being between the most recent value and the immediately preceding value. After the comparison, the immediately preceding value is overwritten by the last value, which is stored until it is overwritten by a new value. It is immaterial for this sequence whether the vehicle stops in the meantime or whether the engine is switched off or not. The most recent average value is retained in the measured value storage device until, after a comparison with a new value, it is overwritten, which takes places irrespective of the result of the comparison. The result of the comparison is the only deciding factor in determining whether or not metering is to take place.
In order to make metering independent of chance fluctuations of the indicated fuel level due to driving, which are impossible to eliminate with absolute certainty in unfavorable driving situations (even by averaging), a certain freely selectable measured value difference must be exceeded before metering is activated. This tolerance threshold can, for example, be determined experimentally and then set to the optimum.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.